In R, use nonstandard evaluation to select specific variables from data.frames

I've got several large-ish data.frames set up like a relational database, and I'd like to make a single function to look for whatever variable I need and grab it from that particular data.frame and add it to the data.frame I'm currently working on. I've got a way to do this that works, but it requires temporarily making a list of all the data.frames, which seems inefficient. I suspect that nonstandard evaluation would solve this problem for me, but I'm not sure how to do it.

Here's what works but seems inefficient:

Table1 <- data.frame(ID = LETTERS[1:10], ColA = rnorm(10), ColB = rnorm(10),
                     ColC = rnorm(10))

Table2 <- data.frame(ID = LETTERS[1:10], ColD = rnorm(10), ColE = rnorm(10),
                     ColF = rnorm(10))

Table3 <- data.frame(ID = LETTERS[1:10], ColG = rnorm(10), ColH = rnorm(10),
                     ColI = rnorm(10))

Key <- data.frame(Table = rep(c("Table1", "Table2", "Table3"), each = 4),
                  ColumnName = c("ID", paste0("Col", LETTERS[1:3]),
                                 "ID", paste0("Col", LETTERS[4:6]),
                                 "ID", paste0("Col", LETTERS[7:9])))

# function for grabbing info from other tables
grab <- function(StartDF, ColNames){

      AllDFs <- list(Table1, Table2, Table3)
      names(AllDFs) <- c("Table1", "Table2", "Table3")

      # Determine which data.frames have that column
      WhichDF <- Key %>% filter(ColumnName %in% ColNames) %>% 
            select(Table)

      TempDF <- StartDF

      for(i in 1:length(ColNames)){
            ToAdd <- AllDFs[WhichDF[i, 1]]
            ToAdd <- ToAdd[[1]] %>% 
                  select(c(ColNames[i], ID))

            TempDF <- TempDF %>% left_join(ToAdd)
            rm(ToAdd)
      }

      return(TempDF)


}

grab(Table1, c("ColE", "ColH"))

What would be great instead would be something like this:

grab <- function(StartDF, ColNames){

      # Some function that returns the column names of all the data.frames
      # without me creating a new object that is a list of them

      # Some function that left_joins the correct data.frame plus the column
      # "ID" to my starting data.frame, again without needing to create that list 
      # of all the data.frames

}